The invention relates generally to the field of fiber reinforced plastic pipe and tubing. More specifically, the invention relates to methods for attaching coupling devices to such pipes and tubing.
Wound-fiber-reinforced plastic products are well known in the art. Some very useful wound-fiber reinforced plastic products include conduit or tubing used to carry fluids. This type of conduit is typically made by winding glass, carbon or other reinforcing fibers about a tube mandrel, a liner or other tube form. The fibers are wound in a substantially helical pattern. The fibers may be impregnated with resin prior to winding or the resin may be applied after winding. The resin is then cured in some manner to create the finished product.
Pipe and tubing is often used in a manner which requires coupling and uncoupling the pipe or tubing at selected locations along the length thereof. One type of releasable coupling known in the art is called an ANSI stub-end flange connector. This type of connector includes a disk-shaped flange having bolt holes arranged in a circle near the circumference of the flange, and a flared xe2x80x9cstub endxe2x80x9d connector, which is compressibly coupled to a corresponding flange and stub end connector by tightening bolts positioned through the bolt holes of both flanges. The stub end connectors may be sealed compressibly against each other by a gasket, o-ring or other sealing device. Typically, the flange and stub end connectors are made of steel or other high strength metal.
Using ANSI stub end flanged connectors known in the art to couple wound fiber reinforced plastic tubing has proven difficult primarily because it is difficult to form a pressure resistant bond to the lining material commonly used in fiber reinforced plastic pipe, and the pipe and the stub end flanged connections have such different bending stiffness that mechanical failure is common.
What is needed is a method for coupling fiber reinforced plastic pipe to a stub end flanged connector that is reliable and strong.
One aspect of the invention is a method for coupling a stub end flanged connector to a fiber reinforced plastic pipe. The method includes tapering an end of the fiber reinforced plastic pipe on the outside surface of its fiber overwrap. An inside surface of the stub end connector is correspondingly tapered. The stub end connector is then bonded to the fiber reinforced plastic pipe. A liner in the plastic pipe is then flared to correspond to a flared end of the stub end connector. Then at least one stiffness transition layer is bonded over the plastic pipe and the stub end connection. The stiffness transition layer extends over an axial span at least including the termination of the stub end connector. One embodiment of the stiffness transition layer includes fiber braid impregnated with resin.
One embodiment of the method of the invention includes bonding a second stiffness transition layer on top of the first stiffness transition layer. The second stiffness transition layer is generally not as long as the first transition layer, but should include in its span the termination of the stub end connector.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.